1,3,5-Triazapentadienes
by Nucleophilic Addition to
1,3- and 1,4-DinitrilesSterically Constrained Examples by
Incorporation into Cyclic Peripheries: Synthesis, Aggregation, and
Photophysical Properties

1,3,5-Triazapentadienes
usually show U- or twisted S-shaped conformations
along the N–C–N–C–N skeleton due to dominating
n/π* interactions. If, however, the 1,3,5-triazapentadiene unit
is part of a ring, its W conformation might be restricted to the plane.
Here, we describe the synthesis of 13 new 1,3,5-triazapentadienes <b>10</b>–<b>12</b>, which are sterically restrained
by incorporation into six- or seven-membered ring systems, by addition
of a lithiated primary amine or hydrazine <b>5</b> to a dinitrile <b>7</b>, <b>8</b>, or <b>9</b> with the two cyano groups
in 1,3 or 1,4 distance. These novel compounds show very strong tendency
for aggregation due to hydrogen bonding, especially to form homodimers
as seen from X-ray data in the solid state. Additional hydrogen bonding
generates also linear chains in the crystal. Several of the new compounds
show fluorescence in solution. Quantum chemical DFT calculations were
used for evaluation of the dimerization energies and for interpretation
of the photophysical properties.